Key table and authorization table management

ABSTRACT

A receiver device consistent with certain embodiments that receives and decrypts digital cable or satellite television signals has a receiver that tunes and demodulates the television signal into a digital transport stream. A decrypter decrypts the digital transport stream using a pair of decryption keys. A first decryption key array stored in a first storage location forming a part of the receiver device, and a second key array stored in a second storage location forming a part of the receiver device, the first and second key arrays representing ordered pairs of keys. An authorization table is stored in a third storage location forming a part of the receiver device, the authorization table containing a mapping, wherein each ordered pair of decryption keys corresponds to a different one of a plurality of Multichannel Video Program Distributors (MVPD). This abstract is not to be considered limiting, since other embodiments may deviate from the features described in this abstract.

CROSS REFERENCE TO RELATED DOCUMENTS

This application is related to U.S. provisional application No.60/688,553 file Jun. 7, 2005, which is hereby incorporated herein byreference.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction of the patent document or thepatent disclosure, as it appears in the Patent and Trademark Officepatent file or records, but otherwise reserves all copyright rightswhatsoever.

BACKGROUND

In digital cable television systems, encryption is commonly used forblocking channels that have not been paid for. Those channels cangenerally only be accessed once an appropriate decryption key isavailable to the customer premise equipment (CPE; e.g., a televisionset-top box (STB), or properly enabled digital television set).Decryption keys are most commonly conveyed to the CPE using entitlementcontrol messages (ECMs) that are transmitted from the network operatoror an equivalent authority to the CPE. The content which is to beprotected is most commonly encrypted using known algorithms such as theadvanced encryption standard (AES), the DVB Common Scrambling Algorithm,the data encryption standard (DES) or its variants. Since theseencryption/decryption algorithms themselves are publicly available, thekey to the security of the content lies in the ability to conceal thedecryption keys necessary to decrypt the content. In most susbscriptionor pay-TV systems, the key-carrying ECMs are transmitted concurrentlywith the content in a single, common data transport strem.

For this reason, decryption keys transmitted via the ECM are commonlyencrypted using proprietary encryption techniques. The encrypted keysare then commonly transmitted to the CPE via the ECM on an inbandchannel, changing on a very frequent basis in order to thwart a hacker'sability to decrypt the content based on an exhaustive trial and errorkey search. Unfortunately, one of the very tools used to thwart thehacker (frequent variation of the key and transmission of ECMscontaining encrypted keys) provides a clue to the hacker to help crackthe encryption algorithm. Each time a key is transmitted, more data isavailable to the hacker that can potentially be used to crack theencryption algorithm itself. Should the algorithm be cracked, thecontent is then unprotected, requiring costly revisions to theencryption algorithm and re-provisioning or even physical replacement ofthe CPE.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain illustrative embodiments illustrating organization and method ofoperation, together with objects and advantages may be best understoodby reference detailed description that follows taken in conjunction withthe accompanying drawings in which:

FIG. 1 is an exemplary key table consistent with certain embodiments ofthe present invention.

FIG. 2 is an exemplary authorization table consistent with certainembodiments of the present invention.

FIG. 3 illustrates the relationship between the exemplary key table andthe exemplary authorization table in a manner consistent with certainembodiments of the present invention.

FIG. 4 illustrates a channel selection process for an encrypted channelin a manner consistent with certain embodiments of the presentinvention.

FIG. 5 is a flow chart of an exemplary process consistent with certainembodiments of the present invention.

DETAILED DESCRIPTION

While this invention is susceptible of embodiment in many differentforms, there is shown in the drawings and will herein be described indetail specific embodiments, with the understanding that the presentdisclosure of such embodiments is to be considered as an example of theprinciples and not intended to limit the invention to the specificembodiments shown and described. In the description below, likereference numerals are used to describe the same, similar orcorresponding parts in the several views of the drawings.

The terms “a” or “an”, as used herein, are defined as one or more thanone. The term “plurality”, as used herein, is defined as two or morethan two. The term “another”, as used herein, is defined as at least asecond or more. The terms “including” and/or “having”, as used herein,are defined as comprising (i.e., open language). The term “coupled”, asused herein, is defined as connected, although not necessarily directly,and not necessarily mechanically. The term “program” or “computerprogram” or similar terms, as used herein, is defined as a sequence ofinstructions designed for execution on a computer system. A “program”,or “computer program”, may include a subroutine, a function, aprocedure, an object method, an object implementation, in an executableapplication, an applet, a servlet, a source code, an object code, ashared library/dynamic load library and/or other sequence ofinstructions designed for execution on a computer system.

The term “program”, as used herein, may also be used in a second context(the above definition being for the first context). In the secondcontext, the term is used in the sense of a “television program”. Inthis context, the term is used to mean any coherent sequence of audiovideo content which would be interpreted as and reported in anelectronic program guide (EPG) as a single television program, withoutregard for whether the content is a movie, sporting event, segment of amulti-part series, news broadcast, etc. The terms “scramble” and“encrypt” and variations thereof are used synonymously herein.

Reference throughout this document to “one embodiment”, “certainembodiments”, “an embodiment” or similar terms means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the presentinvention. Thus, the appearances of such phrases or in various placesthroughout this specification are not necessarily all referring to thesame embodiment. Furthermore, the particular features, structures, orcharacteristics may be combined in any suitable manner in one or moreembodiments without limitation.

The term “or” as used herein is to be interpreted as an inclusive ormeaning any one or any combination. Therefore, “A, B or C” means “any ofthe following: A; B; C; A and B; A and C; B and C; A, B and C”. Anexception to this definition will occur only when a combination ofelements, functions, steps or acts are in some way inherently mutuallyexclusive.

The following Acronyms and Abbreviations may be used herein:

-   BAC Basic Access Control-   BAT Bouquet Association Table-   CA Conditional Access-   CAS Conditional Access System-   CASID Conditional Access System Identifier-   CMTS Cable Modem Termination System-   CPE Customer Premises Equipment-   DOCSIS Data Over Cable System Interface Specification-   DVB Digital Video Broadcast-   ECM Entitlement Control Message-   EMM Entitlement Management Message-   IC Integrated Circuit-   MPEG Moving Pictures Experts Group-   MVPD Multichannel Video Program Distributor-   MSO Multiple System Operator-   NIT Network Information Table-   NTS Network ID, Transport ID and Service ID-   NTSC National Television Standards Committee-   OSD On-Screen Display-   PAT Program Allocation Table-   PID Packet Identifier-   PMT Program Map Table-   PPV Pay-per-View-   PSI Program Specific Information-   QAM Quadrature Amplitude Modulation-   SI Service Information

In order to reduce the exposure of keys in a cable or satellitetelevision system, and in order to significantly simplify the complexityof the management system at both the transmission point and in thecustomer premises equipment, a content key management system is providedin accordance with certain embodiments consistent with the presentinvention.

A content key management structure consistent with certain embodimentsfor a basic access control subsystem is for use in a digital cable orsatellite television system, which augments or preferably, replaces theanalog services on the existing plant with the digital equivalent ofeach analog service.

In traditional CA systems, key epochs are commonly on the order ofmilliseconds, seconds or minutes. The basic access control systemprovides for dynamic replacement of the content keys used toencrypt/decrypt, with a key epoch that may be significantly longer (onthe order of days, weeks or months—if ever) than that used in atraditional CA system, but without the complexity, costs and additionalmessaging systems associated with those systems. Key delivery and CPEauthorization is performed through the delivery of an entitlementmanagement message (EMM), delivered through both (or either) DOCSIS (outof band delivery), for two-way devices, and in-band for supportingone-way devices.

In one embodiment the basic access control schema employed uses at leastone key pair per service tier. Service tiers are groups of individuallogical channels associated with services that are bundled as a discreteentity (“a package”). This methodology is extensible to support servicetiers of any size, including single programs, such as individual events.Access to a particular service tier is determined by whether a supportedCPE device has possession of the appropriate service tier key(s). Tomaintain message security, all EMMs are signed by the network operator'sprivate key so that the received message may be authenticated by the CPEdevice.

FIG. 1 depicts a set of keys for encrypted content that are stored inthe CPE (e.g., a television set-top box) in nonvolatile memory in asecure manner (e.g., using hardware protection against accessing memorycontaining the keys). U.S. Patent publication number US2002/0196939 toUnger, et al. describes an exemplary television set-top box hardware andsoftware that carries out multiple selective decryption. This is anexample of a CPE device that can be suitably modified to carry outprocesses consistent with certain embodiments of the present invention.This publication is hereby incorporated by reference.

The content keys are stored in secure persistent memory and organized asan array or table 12 that constitutes a key library. This library can beaccessed by hardware such as a programmed processor within the CPE asneeded. One arrangement for such a key library is shown in FIG. 1. Thekeys in this example are arranged in m+1 pairs, for use in thedecryption process, with members of the pair being referred to as eitherodd keys 14 or even keys 18. In one example, which should not beconsidered limiting, the keys are 64 bits in length, but 128 bits or anyother suitable key length can be used. Each of the m+1 pairs of keys areindexed with an address reference (which could be a memory address, anactual key number, a name, a key identifier or a memory offset, forexample).

An exemplary structure for the array is as follows: UINT16 key_index;BOOLEAN key_phase; UINT64 content_key[key_index, 2]; if(transport_scrambling_control == ‘10’) key_phase = 0; else if((transport_scrambling_control == ‘11’) key_phase = 1;

The maximum possible storage requirement for this example key structureif it contains every possible 64 bit key is 1 MByte. It is unlikely thata system would currently have need for 65,536 unique keys (32,768 uniquekey pairs), but in the future, it is possible that even more key pairsand keys of greater length may be used. It is, however, anticipated thatfor cable and satellite applications, at least 16,777,216 unique keys(8,388,608 unique key pairs) is preferred at a minimum. Also, multiplelogical channels may be mapped to the same actual key value withoutdeparting from embodiments consistent with this invention. The samecontent key can be used for both audio and video elements of aparticular service, but other variations are also possible.

The association of a particular key pair (even & odd phase) to aspecific service is done through data contained in the table deliveredthrough the program authorization descriptor, mapping a logical channelto a key_index value, which is then used to find the correspondingcontent key pair in the content key table 12. This information iscontained in an Authorization Table 22 as depicted in FIG. 2. Otherembodiments may contain multiple instances of key and authorizationtables, each pair of which corresponds to different networks, such asdifferent MVPDs (e.g. different cable providers, satellite providers andtelephone system operators) provided speculatively for networks that theclient device may at some point be attached to. The authorization table22 also contains a CPE Operation Mask 26 which determines globalfeatures that a particular CPE is to have enabled or disabled whileoperating on the network (e.g., reset, etc.). For each logical channel0−n at 30, there is a service mask 34, which determines which channels aparticular user is authorized to access as well as operationalattributes (such as activation of anti-taping controls, etc.) to beassociated with a particular service, and a key index 38 that associateseach channel with a key pair which is designated for use in decryptingthe channel. The authorization table 22 containing the list of logicalchannels and the associated key indices is also securely stored, as withthe key table 12, in nonvolatile memory within the CPE.

The relationship between the key table 12 and the authorization table 22is illustrated in FIG. 2. In this example, logical channels arecurrently mapped to the key table entries in accordance with thefollowing TABLE 1: TABLE 1 Logical Channel Key index 0 3 1 0 2 m 3 2 . .. . . . n-1 m-1 N m

By mapping a pair of keys stored in the key table 12 to an index to thekeys by channel in authorization table 22, the key for a particularchannel or program can be changed by simply sending an index to the CPEassociated with the channel. In this manner, the working key for aparticular service or group of services can be changed without any riskthat it be exposed through transmission of the key itself by merelysending a new array of key indices via EMM.

Content key delivery can be performed through use of an EMM containing avalid key data descriptor. Content key data is organized as shown inFIG. 1 as a key table 12 containing the pair of content key valuescovering both MPEG encryption phases (even and odd). In non-MPEGembodiments, pairs of keys may also be advantageous, but should not beconsidered limiting. These content key pairs are associated with anindex identifying a particular content key pair. The key data descriptorstructure allows for the en masse replacement of an entire column (evenor odd) of content keys in the table associated with a particularencryption phase. In accordance with certain embodiments, a singledescriptor cannot replace both the content keys in a particular keypair. Two independent EMM messages are separately sent to populate orrefresh the entire content key table 12, one identified as associatedwith the even encryption phase and then one identified as associatedwith the odd encryption phase. In other embodiments, only selected keypairs or individual keys might be provided in the EMM withoutlimitation. The order of these messages is unimportant.

Additionally, an optional element may be employed to increase the levelof indirection in transmitted data. The key index descriptor allows thekey index to be transmitted separately from the program authorizationtable 22 and the key data tables 12. This descriptor is used tooverwrite index data in the program authorization table 22 and can beused to initially provision index data separately or to re-key a systemsolely through transmission of new indices without transmitting key dataor program authorization tables 22. The EMM carying the complete indicesfor a program tier would be very small compared to actual keyreplacement and can likely be contained in a single packet, being ⅓ thesize of the authorization table and at a minimum ¼ the size of the keydata table.

The CPE device should preferably never alter or modify in any way theformat or contents of the data structures containing the programauthorization table 22 and the key data table 12, except to apply theappropriate descriptor data from a validated EMM. The CPE device placesthe data received from the relevant EMM in the exact form and order intothe storage structure without altering the order of entries in thetable. The BAC system provides the logical channel entries in theprogram authorization table in a sorted fashion. Each programauthorization table 22 and the key data table 12 can be transmitted in acomplete form and to replace any existing table in its entirety. Inother embodiments, only selected portions of each table can betransmitted.

In practice, the key data message is used to update only the futurecontent key, which would be the keys associated with the phase oppositeof the one currently being used to encrypt content. This method allowsbackground provisioning of authorized CPEs with the content keys for thenext epoch without any impact upon current device operation. That is tosay for example, if the even key is currently being used, the even keys18 can be replaced so the odd keys are undisturbed for retrieval (andvice versa).

In the illustrative embodiment, content access management is handled inthe following manner with reference to FIG. 4. Channel maps are definedusing a combination of two standard elements. Per the DVB architecture,all RF network resources are defined within the SI construct NetworkInformation Table (NIT). The NIT describes the RF parameters associatedwith each service based upon ‘NTS’ criteria (Network ID, Transport IDand Service ID). The composite value for NTS is unique for every serviceavailable within the system.

The DVB structure Bouquet Association Table (BAT) provides a linkagebetween logical channel numbers and a specific NTS for NIT lookup anddetermination of the necessary RF parameters to access the QAM signalcarrying a desired service. There may be multiple BATs, providingmultiple channel line-ups that could represent differing channel plansbased upon service tier, region, etc. Each BAT has an associated bouquetID that uniquely identifies each BAT. All CPE are assigned an applicablebouquet ID upon provisioning via EMM that indicates the possibleauthorized services that could potentially be accessed by a particularCPE.

By default, all CPE can use a bouquet ID of zero when no bouquet ID hasbeen issued by the headend. There are only two cases that this caseshould be encountered. The first case is when a new device is connectedto the system prior to the headend sending (or the CPE receiving)provisioning. The second case is when an EMM is received from theheadend with an operation mask setting indicating that the CPE should bedeauthorized. The process of deauthorization is defined as deleting thebouquet ID variable along with the contents of the program authorizationtable.

Service access is managed through the program authorization table 22which, as previously noted, is a logical construct maintained within thenonvolatile memory of each CPE device and its contents delivered viaEMMs from the headend. This table 22 contains a list of logical channelsthat the particular device is permitted to access, along with the keyindex and other data uniquely associated with each service. The presenceof a logical channel in the channel list contained within the programauthorization table 22 provides an indication that the channel is acandidate for viewing on a particular CPE, but does not in itselfguarantee access.

Each program authorization table 22 is transmitted via EMM to the CPEdevice in a complete form in the preferred embodiment to replace anyexisting table contents in its entirety. In this embodiment, no partialchannel maps are transmitted and received table data is never appendedwithin the CPE. In this embodiments, the EMM containing the programauthorization table information will not contain the associated serviceand operation masks. These items are delivered by separate EMMs and arecomposited by the CPE onto the program authorization table 22. However,other embodiments will occur to those skilled in the art uponconsideration of the present teachings.

Two other components, combined with the presence of a service's logicalchannel number in the program authorization table, control the ultimatedetermination of whether the CPE should be able to access a particularservice. One component is the channel_unauthorized bit contained withinthe service_mask variable associated with each logical channel entry inthe program authorization table 22. If this bit is set, accomplishedthrough an EMM, then the particular channel is deauthorized and notavailable for viewing. The other controlling components are theCPE_deauthorized and brick_mode bits contained within the CPEoperation_mask, which controls attributes for the entire CPE. It too ismanaged through EMM messages and is part of the program authorizationtable 22 structure.

The process of accessing a particular service is illustrated in FIG. 4and FIG. 5 Error! Reference source not found and follows the subsequentlogic (referencing identifiers for both figures):

A viewer indicates the desire to change decoded AN service through theirremote control or other user interface at 50 and 150. For example, thiscan be accomplished by a channel up/down command or a direct logicalchannel number entry.

-   1. A computer program application (Access Logic Software 52) running    on the CPE receives, decodes and validates the user command at 154.-   2. At 158, the CPE application checks the value of the    operation_mask 26 contained within the program authorization table    22 to see if either the CPE_deauthorized or brick mode bits are set.    If the either of these bits are set, further processing of the    request is ended at 160. If the bouquet_id is set to zero (default)    at 164, then the process continues to 168 without further reference    to the program authorization table 22 for access to free or barker    channels in an unprovisioned CPE and goes directly to item 6 below.    Otherwise, the process proceeds to 3 below.-   3. The CPE application parses the logical_channel field of the    program authorization table at 168 using the following index:-   a. For channel up/down, use current channel number as the search    index. When the match is found, increment or decrement one entry as    appropriate to reach the entry for the target channel.-   b. For direct entry, use the entered logical channel value as an    index for the target channel. If the desired target channel is not    contained within the table, display and appropriate OSD informing    viewer.-   4. From the program authorization table 22, the CPE Access Logic    Software application 52 obtains the service mask field associated    with the logical channel entry in the program authorization table 22    at 172 and checks to see if the channel_unauthorized bit is set at    176. If this bit is set at 176, then further processing of the    request is ended at 160. The CPE Access Logic Software application    also obtains the key index value at 180 associated with the    requested service from the same record in the program authorization    table containing the target logical_channel value.-   5. Using the key_index value associated with the requested service,    the CPE Access Logic Software application 52 accesses the key table    12 stored in nonvolatile memory at 184, using the key_index value as    the array index to obtain the two 64-BIT DVB-CSA working keys used    to encrypt the content. (In the example shown in FIG. 4, the key    index points to keys indexed at the 0 position.) The key pair values    are loaded by the CPE Access Logic Software application in the CPE    transport decryption subsystem (descrambler 56) for content    decryption.-   6. The CPE Access Logic Software application 52 parses the BAT image    60 at 168 stored in RAM, using the logical_channel and bouquet_id    values as paired indices. When the entry in the table matching both    criteria is found, the associated network_id, transport_id and    service_id values (referred to collectively as ‘NTS’) are obtained    from the cached bouquet allocation table (BAT).-   7. The CPE Access Logic Software application 52 next (at 188) parses    the NIT image 64 stored in RAM, using the NTS values obtained from    the BAT as composite indices. When the entry in the table matching    all criteria is found, the associated frequency, modulation and PAT    PID information are obtained from the table. The data obtained are    then used by the CPE Access Logic Software application to provision    the tuner and demodulator 68 and transport processor 72 subsystems    to access the transport containing the requested service.

The CPE executes the tuning process and then follows the standard MPEGprocedure using the service_id of the requested service and thetransport PSI data tree to determine and use the respective audio andvideo resources of the transport multiplex to decode the desired serviceat 192.

The EMM format supports both unit (singular) and group messages and boththe definition of and membership within a group can be arbitrarilydefined. The CPE devices under BAC management are able to belong tomultiple groups and each device by default belongs to two groups: itself(unit) and a global group encompassing all devices. The EMM isstructured as a standard MPEG private section, containing one or moredescriptors. The descriptors provide specific direction to the CPEregarding channel authorization, key delivery, software downloadcommands, group membership, emergency alerts, etc. Regardless of numberor type of descriptors contained within the EMM, each message is bothencrypted using a global, fixed key and validated through acryptographic signature.

Every known cryptographic system for cable and satellite systems has aroot secret stored somewhere inside the CPE client. In traditional CAsystems, this is done with either smart cards, dedicated custom ICs orthrough other means to create an electrically and mechanically secureenvironment to store the root secrets. The basic access control systemdoes not use these extremely complex schemes nor incurs the associatedhardware and licensing costs. The system contains four root secrets thatare stored within the CPE. In order to compromise the system, all fourmust be known. The root secrets are the respective key pairs for the EMMand software download transport encryption and the keys for both thesoftware download and EMM HMAC algorithms, respectively.

In one embodiment, the basic access control (BAC) schema uses at leastone key pair per service tier. Service tiers are groups of individuallogical channels associated with services that are bundled as a discreteentity (“package”). This methodology is extensible to support servicetiers of any size, including single programs, such as individual events.Access to a particular service tier is determined by whether a supportedCPE device has possession of the appropriate service tier key(s). Tomaintain message security, all EMMs are signed by the service provider'sprivate key so that the received message may be authenticated by the CPEdevice.

In addition, entitlement (authorization) to individual services isdetermined through a service_mask, matched to each service with anauthorization bit carried in the mask in an “opt-out” fashion. If aparticular service bit is one in table 22, the content represented bythe bit is non-authorized. The service_mask is maintained in nonvolatilememory in authorization table 22 within each supported CPE device and islocally modified through data carried in authenticated EMMs to reflectthe services that a particular CPE device is intended to access. Thisarrangement, while reinforcing the key-per-tier schema, also allowsimplementation of á la carte programming. This schema also allows forthe removal of programming upon a subscriber's request that they maywant eliminated.

In accordance with certain embodiments, three types of keys are definedand employed: emm_key, download_key and content_key. In one particularembodiment, the emm_key is a pair of 64-bit values that are fixed andused to decrypt all DVB-CSA encrypted EMM messages received by the CPE,though any appropriate key length and encryption algorithm may beemployed. This key has the same value for all CPE devices. These emm_keyvalues are permanently stored in the CPE in a secure manner. In oneexample embodiment, the download_key is a pair of 64-bit values that arealso fixed and are used to decrypt all DVB-CSA. encrypted SBS-downloadcontent messages received by the CPE, though any appropriate key lengthand encryption algorithm may be employed. The same values are used forall CPE devices. These values are also permanently stored in the CPE ina secure manner. The content keys are the keys used for decryption ofthe encrypted content. Content keys are stored in the CPE in nonvolatilememory in a secure manner. The content keys are organized as an array,as shown previously in FIG. 1 for certain embodiments.

In accordance with certain embodiments, the content keys may be fixed inmemory at the time of provisioning or manufacture. In other embodiments,as described above, the keys may be dynamically delivered at anysuitable interval. Since there are many keys available for decryption,replacing the keys does not have to be done as often as in conventionalcable systems. Likewise, the authorization table 22 containing thelogical_channel, key_index and service_mask values can either beprovided as a hardcoded table of constants or can be dynamically changedby use of transmission of channel authorization descriptors had in anEMM.

Hence, in certain embodiments, the content key can be changed on aregular basis by simply transmitting EMM messages containing new indexvalue associations between the logical channel and the contentdecryption key pair. Electronic signatures can be employed toauthenticate entitlement messages and software download messages. Eachdevice can be addressed globally, individually or by group or servicetier. Additionally, it is noted that there may be any number m+1 ofcontent key pairs stored in table 12. The association between logicalchannels and content keys need not be 1:1. For example, multiplechannels may be associated with a single key, and certain keys may notbe associated with any channels at all at any given time. By providingan abundant library of keys, the decryption of content can be altered bychanging the key index associated with a particular logical channel.This can be accomplished at any time for a single channel, multiplechannels or all channels.

In accordance with certain embodiments, EMMs can be delivered through atleast two independent mechanisms. The first delivery method, which isparticularly useful for two-way devices, is through the use of theDOCSIS compliant cable modem integral to two-way CPE devices (e.g.,set-top boxes). A second delivery method that can be provided forone-way devices and as an alternate method for two-way devices isin-band delivery, duplicated on each transport stream. The in-banddelivery can for example closely follow the MPEG prescribed method.

A conditional access table (CAT), as defined in ISO/IEC 13818-1, can becarried in each transport stream and transmitted with the system SI datavia DOCSIS delivery using UDP multicast. The CAT can contain one or moreCA descriptors, as required by the standard. One of the CA descriptorscan have the CASID of the system and the table also provides the EMM PIDassignment within a particular transport stream. In this case, the CPEconfigures its transport processing elements to receive EMMs carried onthis PID. For devices that receive SI through OOB methods such asDOCSIS, the EMM data can be carried on a multicast IP address and portspecified in the CAT message, but the rest of the process and syntaxremains unchanged from the in-band process.

The EMM can use, for example, the following format:

-   table_id: An 8-bit field that is set to 0×82 to identify this    private table uniquely as a unit addressed EMM or to 0×84 to    identify this private table uniquely as a group addressed EMM.-   section_syntax_indicator: A 1-bit field that is set to 0 to identify    this table as a private section. The following bit set to zero    signifies the data payload as private data.-   address_hash: A 16-bit field carrying the hashed value of either the    unit or group address, depending upon the table_id value. The entire    48-bit address field shall be condensed into a single 16-bit value    using the 32-bit FNV-1 hash with xor-folding. This parameter is    provided as a method to allow hardware filtering of EMMs and reduce    CPE processor workload.-   version: a 5 bit field that is monotonically increased for each    unique EMM transmitted to a particular addressee or group, as    applicable.-   address: A 48-bit field carrying either the unit or group address,    depending upon the table_id value. This is the same value used to    create the address_hash.

The EMM message carries one or more MPEG format descriptors, whichcontain the actual entitlement payload. Every EMM has at least asignature data descriptor, which is always the last descriptor in anEMM. The inclusion of any descriptors in addition to the signature datadescriptor is optional and there is no limitations regarding the numberor order of the optional descriptors.

The EMM section is marked as an MPEG private section containing privatedata. For MPEG, each EMM section cannot exceed 4096 bytes in length. Ifthe total message payload exceeds 4096 bytes, then multiple sections aretransmitted and the payload spans sections, with the section_number andlast_section_number indicating where a particular section fits in thesequence. In a multi-section EMM, each section is not terminated with a4 byte CRC for that particular section. The last section in the messagecontains a CRC covering the composite payload. It is the responsibilityof the receiving device to buffer a multi-section EMM in the correctsequential order and to remove the intervening section headers beforeEMM payload concatenation and composite CRC validation.

In accordance with certain embodiments, each CPE will initially beprovisioned for services through reception of an EMM carrying at aminimum a group address assignment and FIPS assignment descriptor. TheSTB will receive an assignment to a group address carrying the “supergroup” address applicable to that CPE. The EMM carried in the “supergroup” typically carries only version and signature descriptors. Theversion descriptor includes other group addresses pointing to the keylist and program authorization tables appropriate to that CPE based uponservice tier, CPE type, region and/or locality.

The key data descriptor is a private descriptor providing the array ofworking keys used for decrypting content. Its format is defined for theillustrative embodiment in TABLE 2 below. TABLE 2 Syntax No. of BitsIdentifier key_data_descriptor( ){ descriptor_tag 8 uimsbfdescriptor_length 32 uimsbf key_phase 1 bslbf reserved 7 bslbf key_count16 uimsbf for (i=0; i<key_count;i++) { 64 uimsbf content_key } }

This table uses the following variables:

-   descriptor_tag: An 8-bit field that is set to 0×B2 to identify this    descriptor uniquely as a key data descriptor.-   descriptor_length: A 32-bit field specifying the number of bytes    immediately following the descriptor length field, up to the end of    this descriptor.-   key_phase: A single bit field that when set to a ‘1’, indicates that    the following array data is applied to packets carrying a transport    scrambling_control value of ‘11’. If the bit is cleared to a ‘0’, it    indicates that the following array data is applied to packets    carrying a transport_scrambling control value of ‘12’.-   key_count: A 16-bit field containing the number of entries in the    content key array-   content_key: A 64-bit value containing one DVB-CSA content key.

The signature data descriptor is a private descriptor providing thesignature payload used for authentication of an EMM message. Its formatis defined in TABLE 3 below. TABLE 3 Syntax No. of Bits Identifiersignature_data_descriptor( ){ descriptor_tag 8 uimsbf descriptor_length32 uimsbf EMM_signature 160 uimsbf }

In TABLE 3, the following variables are used:

-   descriptor_tag: An 8-bit field that is set to 0×B3 to identify this    descriptor uniquely as a signature data descriptor.-   descriptor_length: A 32-bit field specifying the number of bytes    immediately following the descriptor length field, up to the end of    this descriptor. For this particular descriptor, the value is    defined to be 0×14.-   EMM_signature A 160-bit field carrying the EMM message    authentication code.

The program authorization descriptor is a private descriptor carryingthe information used to provision the CPE to receive program contenttiers. Its format for the example embodiment is defined in TABLE 4below. TABLE 4 No. of Syntax Bits Identifierprogram_authorization_descriptor( ){ descriptor_tag 8 uimsbfdescriptor_length 32 uimsbf bouquet_id 16 uimsbf reserved 16 uimsbfchannel_count 16 uimsbf for (i'0; i<channel_count;i++) { logical_channel16 uimsbf reserved 16 uimsbf key_index 16 uimsbf } }

TABLE 4 uses the following variables:

-   descriptor_tag: An 8-bit field that is set to 0×B5 to identify this    descriptor uniquely as a program authorization descriptor.-   descriptor_length: A 32-bit field specifying the number of bytes    immediately following the descriptor_length field, up to the end of    this descriptor.-   bouquet_id: A 16-bit field carrying the index to the assigned    channel bouquet as defined in the BAT table.-   channel count: A 16-bit field indicating the size of the channel    array following this variable.-   logical_channel: A 16-bit field specifying a logical channel number.    The logical channel identified in this field is paired to the    service_mask, carried in the service_mask descriptor, field as a    record pair.

The data contained within array is stored in CPE nonvolatile memory. Inthe case where the array has not been received or is an entry for aparticular channel otherwise missing, the default value is set to, forexample, 0×00.

-   key_index: A 16-bit field specifying a pointer to an element in the    data structure, stored in CPE nonvolatile memory containing the    content keys for the service. Both the audio and video portions of a    given service use the same content encryption key in this    embodiment, but this should not be considered limiting.

The service mask descriptor is a private descriptor carrying theinformation used to change the attributes associated with the servicesprovisioned in a CPE and stored in nonvolatile memory as part of theprogram authorization table structure. It is a subset of the programauthorization descriptor. Its format, for the example embodiment isdefined in TABLE 5 below. TABLE 5 Syntax No. of Bits Identifierservice_mask_descriptor( ){ descriptor_tag 8 uimsbf descriptor_length 32uimsbf item_count 16 uimsbf for (i=0; i<item_count;i++) { 16 uimsbflogical_channel 16 uimsbf service_mask } }

TABLE 5 uses the following variables:

-   descriptor_tag: An 8-bit field that is set to 0×BB to identify this    descriptor uniquely as a service mask descriptor.-   descriptor_length: A 32-bit field specifying the number of bytes    immediately following the descriptor length field, up to the end of    this descriptor.-   item_count: A 16-bit field indicating the number of entries in the    list following this variable.-   logical_channel: A 16-bit field specifying a logical channel number.    The logical channel identified in this field will be paired to the    subsequent service_mask field as a record pair

service_mask: A 16-bit field containing a binary mask indicatingattributes associated with the corresponding logical channel. ServiceMask Bits are defined in accordance with TABLE 6 below. TABLE 6 PositionMask Bit Definition (Set) 0x0000 Clears all previous mask bits 0x0001Channel Unauthorized 0x0002 Macrovision Activated 0xFFFC to 0x0004ReservedThe data contained within this array is stored in CPE nonvolatilememory. In the case where the array has not been received or is an entryfor a particular channel otherwise missing, the default value can be setto 0×00.

The BAT descriptor is a private descriptor carrying the informationnecessary to provision the CPE to receive program content tiers bychanging the value of the bouquet_id variable stored within the CPEnonvolatile memory as part of the program authorization table structure.It is a subset of the program authorization descriptor. Its format isdefined in TABLE 7 below. TABLE 7 Syntax No. of Bits Identifierbouquet_descriptor( ){ descriptor_tag 8 uimsbf descriptor_length 32uimsbf bouquet_id 16 uimsbf }

TABLE 7 uses the following variables:

-   descriptor_tag: An 8-bit field that can be set to 0×BC to identify    this descriptor uniquely as a bouquet descriptor.-   descriptor_length: A 32-bit field specifying the number of bytes    immediately following the descriptor_length field, up to the end of    this descriptor.-   bouquet_id: A 16-bit field carrying the index to the assigned    channel bouquet as defined in the BAT table.

Thus, a receiver device consistent with certain embodiments thatreceives and decrypts digital cable or satellite television signals hasa receiver that tunes and demodulates the television signal into adigital transport stream. A decrypter decrypts the digital transportstream using a pair of decryption keys. A first decryption key arraystored in a first storage location forming a part of the receiverdevice, and a second key array stored in a second storage locationforming a part of the receiver device, the first and second key arraysrepresenting ordered pairs of keys. An authorization table is stored ina third storage location forming a part of the receiver device, theauthorization table containing a mapping, wherein each ordered pair ofdecryption keys corresponds to a different one of a plurality ofMultichannel Video Program Distributors (MVPD). Any of the first, secondand third storage locations may or may not be a part of a single memorydevice.

Another receiver device that receives and decrypts digital cable orsatellite television signals has a receiver that tunes and demodulatesthe television signal into a digital transport stream. A decrypterdecrypts the digital transport stream using a pair of decryption keyscomprising an even key and an odd key, wherein the even and odd keys arealternately used by the decrypter for decryption during successive keyepochs. A key table is stored in a first secure persistent storagemedium forming a part of the receiver device, the key table containing alibrary of a plurality of even keys and an associated plurality of oddkeys forming key pairs that are indexed with a key identifier. Anauthorization table is stored in a second secure persistent storagemedium forming a part of the receiver device, the authorization tablecontaining a mapping of a logical channel to a key pair identifier foreach of a plurality of logical channels. At least a portion of contentsof the authorization table is received in a first encrypted privateEntitlement Management Message (EMM) message in order to establish themapping of a logical channel to a key pair identifier. In response to auser input for selecting one of the plurality of logical channels in theauthorization table a key index associated with the selected logicalchannel is identified, and the key index is used to select a key pairfrom the key table for use by the decrypter in decrypting the transportstream.

A method, consistent with certain embodiments, of enabling a receiverdevice to decrypt digital satellite or television signals involvesstoring a plurality of key pairs in a key table in secure persistentstorage in the receiver device, with each key pair corresponding to akey index; receiving a first private Entitlement Management Message(EMM) at the receiver device containing a mapping of at least onelogical channel to a key index identifying a key pair associated usedfor decrypting the logical channel; storing the mapping in anauthorization table along with information indicating whether or not thereceiver device is authorized to receive the logical channel; receivinga command to tune to a specified logical channel; referencing theauthorization table to determine if the receiver device is authorized totune to the tuning the receiver device to the specified logical channel;if the receiver device is authorized to tune to the specified logicalchannel, tuning to the specified channel and demodulating a digitaltransport stream; referencing the authorization table to retrieve thekey pair mapped to the logical channel; and decrypting the transportstream using the key pair, with one key of the key pair being used at atime.

Those skilled in the art will recognize, upon consideration of the aboveteachings, that certain of the above exemplary embodiments are basedupon use of a programmed processor. However, the invention is notlimited to such exemplary embodiments, since other embodiments could beimplemented using hardware component equivalents such as special purposehardware and/or dedicated processors. Similarly, general purposecomputers, microprocessor based computers, micro-controllers, opticalcomputers, analog computers, dedicated processors, application specificcircuits and/or dedicated hard wired logic may be used to constructalternative equivalent embodiments.

Software and/or firmware embodiments may be implemented using aprogrammed processor executing programming instructions that in certaininstances are broadly described above in flow chart form that can bestored on any suitable electronic or computer readable storage medium(such as, for example, disc storage, Read Only Memory (ROM) devices,Random Access Memory (RAM) devices, network memory devices, opticalstorage elements, magnetic storage elements, magneto-optical storageelements, flash memory, core memory and/or other equivalent volatileand. non-volatile storage technologies) and/or can be transmitted overany suitable electronic communication medium. However, those skilled inthe art will appreciate, upon consideration of the present teaching,that the processes described above can be implemented in any number ofvariations and in many suitable programming languages without departingfrom embodiments of the present invention. For example, the order ofcertain operations carried out can often be varied, additionaloperations can be added or operations can be deleted without departingfrom certain embodiments of the invention. Error trapping can be addedand/or enhanced and variations can be made in user interface andinformation presentation without departing from certain embodiments ofthe present invention. Such variations are contemplated and consideredequivalent.

While certain illustrative embodiments have been described, it isevident that many alternatives, modifications, permutations andvariations will become apparent to those skilled in the art in light ofthe foregoing description.

1. A receiver device that receives and decrypts digital cable orsatellite television signals, comprising: a receiver that tunes anddemodulates the television signal into a digital transport stream; adecrypter that decrypts the digital transport stream using a pair ofdecryption keys comprising an even key and an odd key, wherein the evenand odd keys are alternately used by the decrypter for decryption duringsuccessive key epochs; a key table stored in a first secure persistentstorage medium forming a part of the receiver device, the key tablecontaining a library of a plurality of even keys and an associatedplurality of odd keys forming key pairs that are indexed with a keyidentifier; an authorization table stored in a second secure persistentstorage medium forming a part of the receiver device, the authorizationtable containing a mapping of a logical channel to a key pair identifierfor each of a plurality of logical channels; wherein, at least a portionof contents of the authorization table is received in a first encryptedprivate Entitlement Management Message (EMM) message in order toestablish the mapping of a logical channel to a key pair identifier; andmeans responsive to a user input for selecting one of the plurality oflogical channels in the authorization table to identify a key indexassociated with the selected logical channel, and for further using thekey index to select a key pair from the key table for use by thedecrypter in decrypting the transport stream.
 2. The receiver deviceaccording to claim 1, further comprising a DOCSIS modem forming a partof the receiver device, and wherein the first EMM is received by thereceiver device over the DOCSIS modem via an out of band channel.
 3. Thereceiver device according to claim 1, wherein the first EMM is receivedby the receiver device using an inband channel.
 4. The receiver deviceaccording to claim 1, wherein at least a portion of the contents of thekey table is received in a second encrypted private (EMM) message. 5.The receiver device according to claim 4, further comprising a DOCSISmodem forming a part of the receiver device, and wherein the second EMMis received by the receiver device over the DOCSIS modem via an out ofband channel.
 6. The receiver device according to claim 4, wherein thesecond EMM is received by the receiver device using an inband channel.7. The receiver device according to claim 1, wherein the encryptedprivate EMM message updates the key table and contains a collection ofeither odd keys or even keys only, whereby, no single EMM message forupdating the key table contains both odd keys and even keys.
 8. Thereceiver device according to claim 1, wherein at least a portion of thelibrary of keys in the key table is replaced by receipt of a pair ofencrypted private EMM message, with one containing replacement odd keysthe other containing replacement even keys.
 9. The receiver deviceaccording to claim 1, wherein a new set of odd keys is only stored inthe key table during a time when an odd key is currently in use by thedecrypter, and wherein a new set of even keys is only stored in the keytable during a time when an even key is currently in use by thedecrypter.
 10. The receiver device according to claim 1, wherein the keytable entries are initially populated during a provisioning process. 11.The receiver device according to claim 1, wherein the key table entriesare initially populated at a time of manufacture.
 12. The receiverdevice according to claim 1, wherein the authorization table furthercomprises a service mask entry for each logical channel that determinesthe receiver device's authorization to receive each logical channel. 13.The receiver device according to claim 1, wherein the authorizationtable further comprises an operation mask that determines whether or notthe receiver device is authorized to operate on a specified network. 14.The receiver device according to claim 1, wherein the authorizationtable contains global attributes of the receiver device.
 15. Thereceiver device according to claim 1, wherein the authorization tablecontains a service attribute for at least on channel.
 16. The receiverdevice according to claim 1, wherein the first secure persistent storagemedium and the second secure persistent storage medium comprise separateportions of a single storage device.
 17. The receiver device accordingto claim 1, wherein the first and second secure persistent storagemedium are mechanically secured within the receiver device such that thekey table and the authorization table are inaccessible in unencryptedform.
 18. The receiver device according to claim 1, wherein the keytable contains at least about 8,000,000 unique key pairs.
 19. A receiverdevice that receives and decrypts digital cable or satellite televisionsignals, comprising: a receiver that tunes and demodulates thetelevision signal into a digital transport stream; a decrypter thatdecrypts the digital transport stream using a pair of decryption keys; afirst decryption key array stored in a first storage location forming apart of the receiver device, a second key array stored in a secondstorage location forming a part of the receiver device, the first andsecond key arrays representing ordered pairs of keys; an authorizationtable stored in a third storage location forming a part of the receiverdevice, the authorization table containing a mapping, wherein eachordered pair of decryption keys corresponds to a different one of aplurality of Multichannel Video Program Distributors (MVPD).
 21. Thereceiver device according to claim 20, wherein at least a portion ofcontents of the authorization table is received in a first encryptedprivate Entitlement Management Message (EMM) message in order toestablish the mapping.
 22. The receiver device according to claim 20,further comprising means responsive to a user input for selecting one ofthe plurality MVPDs to identify an ordered pair of decryption keys usingthe mapping in the authorization table.
 23. The receiver deviceaccording to claim 20, wherein the authorization table further comprisesa service mask entry for each MVPD that determines the receiver device'sauthorization to receive content from each MVPD.
 24. The receiver deviceaccording to claim 20, wherein the authorization table further comprisesan operation mask that determines whether or not the receiver device isauthorized to operate on a specified network.
 25. The receiver deviceaccording to claim 20, wherein the authorization table contains globalattributes of the receiver device.
 26. The receiver device according toclaim 20, wherein the service mask authorization table contains aservice attribute for at least on channel.
 27. A receiver device thatreceives and decrypts digital cable or satellite television signals,comprising: a receiver that tunes and demodulates the television signalinto a digital transport stream; a decrypter that decrypts the digitaltransport stream using a pair of decryption keys comprising an even keyand an odd key, wherein the even and odd keys are alternately used bythe decrypter for decryption during successive key epochs; a key tablestored in a first secure persistent storage medium forming a part of thereceiver device, the key table containing a library of a plurality ofeven keys and an associated plurality of odd keys forming key pairs thatare indexed with a key identifier, wherein the key table entries areinitially populated during a provisioning process; wherein at least aportion of the library of keys in the key table is replaced by receiptof a first encrypted private EMM message that contains replacement oddkeys and receipt of a second encrypted private EMM message that containsreplacement even keys, and wherein a new set of odd keys is only storedin the key table during a time when an odd key is currently in use bythe decrypter, and wherein a new set of even keys is only stored in thekey table during a time when an even key is currently in use by thedecrypter; an authorization table stored in a second secure persistentstorage medium forming a part of the receiver device, the authorizationtable containing a mapping of a logical channel to a key pair identifierfor each of a plurality of logical channels; wherein the authorizationtable further comprises a service mask entry for each logical channelthat determines the receiver device's authorization to receive eachlogical channel, and wherein the authorization table further comprisesan operation mask that determines whether or not the receiver device isauthorized to operate on a specified network; wherein, at least aportion of contents of the authorization table is received in a thirdencrypted private Entitlement Management Message (EMM) message in orderto establish the mapping of a logical channel to a key pair identifier;means responsive to a user input for selecting one of the plurality oflogical channels in the authorization table to identify a key indexassociated with the selected logical channel, and for further using thekey index to select a key pair from the key table for use by thedecrypter in decrypting the transport stream;
 28. The receiver deviceaccording to claim 27, further comprising a DOCSIS modem forming a partof the receiver device, and wherein the EMM messages are received by thereceiver device over the DOCSIS modem via an out of band channel. 29.The receiver device according to claim 27, wherein the EMM messages arereceived by the receiver device using an inband channel.
 30. Thereceiver device according to claim 27, wherein the first securepersistent storage medium and the second secure persistent storagemedium comprise separate portions of a single storage device.
 31. Thereceiver device according to claim 27, wherein the first and secondsecure persistent storage medium are mechanically secured within thereceiver device such that the key table and the authorization table areinaccessible in unencrypted form.
 32. The receiver device according toclaim 27, wherein the key table contains at least about 8,000,000 uniquekey pairs.
 33. A method of enabling a receiver device to decrypt digitalsatellite or television signals, comprising: storing a plurality of keypairs in a key table in secure persistent storage in the receiverdevice, with each key pair corresponding to a key index; receiving afirst private Entitlement Management Message (EMM) at the receiverdevice containing a mapping of at least one logical channel to a keyindex identifying a key pair associated used for decrypting the logicalchannel; storing the mapping in an authorization table along withinformation indicating whether or not the receiver device is authorizedto receive the logical channel; receiving a command to tune to aspecified logical channel; referencing the authorization table todetermine if the receiver device is authorized to tune to the tuning thereceiver device to the specified logical channel; if the receiver deviceis authorized to tune to the specified logical channel, tuning to thespecified channel and demodulating a digital transport stream;referencing the authorization table to retrieve the key pair mapped tothe logical channel; and decrypting the transport stream using the keypair, with one key of the key pair being used at a time.
 34. The methodaccording to claim 33, wherein the receiver device comprises a DOCSISmodem, and wherein the first EMM is received by the receiver device overthe DOCSIS modem via an out of band channel.
 35. The method according toclaim 33, wherein the first EMM is received by the receiver device usingan inband channel.
 36. The method according to claim 33, wherein atleast a portion of the contents of the key table is received in a secondencrypted private (EMM) message.
 37. The method according to claim 36,wherein the receiver device further comprises a DOCSIS modem, andwherein the second EMM is received by the receiver device over theDOCSIS modem via an out of band channel.
 38. The method according toclaim 36, wherein the second EMM is received by the receiver deviceusing an inband channel.
 39. The method according to claim 36, whereinthe second encrypted private EMM message updates the key table andcontains a collection of either odd keys or even keys only, whereby, nosingle EMM message for updating the key table contains both odd keys andeven keys.
 40. The method according to claim 36, wherein at least aportion of the keys in the key table is replaced by receipt of a pair ofencrypted private EMM message, with one containing replacement odd keysthe other containing replacement even keys.
 41. The method according toclaim 33, wherein a new set of odd keys is only stored in the key tableduring a time when an odd key is currently in use by the decrypter, andwherein a new set of even keys is only stored in the key table during atime when an even key is currently in use by the decrypter.
 42. Themethod according to claim 33, wherein the authorization table furthercomprises a service mask entry for each logical channel that determinesthe receiver device's authorization to receive each logical channel. 43.The method according to claim 33, wherein the authorization tablefurther comprises an operation mask that determines whether or not thereceiver device is authorized to operate on a specified network.
 44. Acomputer readable storage medium storing instructions which, whenexecuted on a programmed processor, carry out a process according toclaim 33.